The electronic apparatuses using a motor therein include information recording/playback apparatuses. The application of the hard disc drive unit included in such information recording/playback apparatuses has become wider and wider. Namely, it is used not only as a recorder in a large information processor and desktop personal computer, but also in electronic apparatuses such as a notebook-sized personal computer, smaller-size portable terminal, etc.
Recently, there is available a PC (personal computer) card type hard disc drive unit whose size is approximately the size of a PC card-sized IC (integrated circuit) memory card or a card type modem. When using the PC card type hard disc drive unit, the user inserts it into a notebook-sized PC or portable terminal through a PC card slot provided in the latter.
The hard disc drive unit is provided with a spindle motor to drive a hard disc which records information signals. The spindle motor supports a spindle rotatably by means of a bearing unit. The bearing unit uses a dynamic-pressure fluid bearing whose frictional resistance is small and which allows the spindle to rotate with less load. Such a dynamic-pressure fluid bearing unit will be described with reference to FIG. 1.
In FIG. 1, the bearing unit using the dynamic-pressure fluid bearing is generally indicated with a reference 1060. The bearing unit 1060 shown in FIG. 1 is to support a shaft generally indicated with a reference 1061. This shaft 1061 consists mainly of a shaft body 1068 and a radial projection 1069 formed at one end (thrusting-directional end) of the shaft body 1068 in the form of a disc larger in diameter than the shaft body 1068. The bearing unit 1060 itself includes a radial bearing 1062 which supports the shaft body 1068 of the shaft 1061 circumferentially of the latter, a thrust bearing 1063 which supports the radial projection 1069 formed at the thrusting-directional end of the shaft 1061, and a housing 1064 which contains and supports the radial bearing 1062 and thrust bearing 1063.
The radial bearing 1062 has formed in the inner surface thereof opposite to the outer surface of the shaft body 1068 a pair of first dynamic pressure producing recesses 1062a. Also the radial bearing 1062 has a second dynamic pressure producing recess 1062b formed in the end surface thereof opposite to the radial projection 1069 of the shaft 1061. The thrust bearing 1063 has a third dynamic pressure producing recess 1063a formed in the surface thereof opposite to the radial projection 1069 of the shaft 1061. Each of these dynamic pressure producing recesses 1062a, 1062b and 1063a is a herringbone-shaped recess formed from a V-shaped pair of recesses joined to each other by a coupling recess in the rotating direction of the shaft 1061.
The housing 1064 containing and supporting the radial bearing 1062 and thrust bearing 1063 which support together the shaft body 1068 is formed to have a cylindrical shape open at either end thereof. The housing 1064 is closed by a bottom closing member 1065 at the end thereof where the thrust bearing 1063 is disposed. At the end (top end) of the housing 1064 opposite to the end where the thrust bearing 1063 is disposed, there is installed a top closing member 1066 in which a shaft insertion hole 1067 is formed through which the body 1068 of the shaft 1061 is passed.
The shaft 1061 is rotatably supported in the housing 1064 with the body 1068 thereof being received in the radial bearing 1062 and the radial projection 1069 provided at the bottom end of the shaft 1061 being supported on the thrust bearing 1063. The shaft 1061 has the top end portion of the body 1068 thereof projected out of the housing 1064 through the shaft insertion hole 1067.
The housing 1064 is filled with a lubricant which is a viscous fluid. When the shaft 1061 is rotated, the lubricant is circulated through the first and second dynamic pressure producing recesses 1062a and 1062b to produce a dynamic pressure.
A joint 1071 between the housing 1064 filled with the viscous fluid and the top closing member 1066 and a joint 1072 between the housing 1064 and bottom closing member 1065, are completely sealed with an adhesive to prevent the lubricant filled in the housing 1064 from leaking out. The inner surface of the top closing member 1066 is applied with a surfactant to prevent the lubricant from moving from the shaft insertion hole 1067 to outside the housing 1064 under the action of a centrifugal force developed due to the rotation of the shaft 1061.
As mentioned above, the shaft 1061 used in the bearing unit 1060 includes the shaft body 1068 and disc-shaped radial projection 1069, and there is a large gap 1070 between the inner surface of the housing 1064 and end face of radial projection 1069.
In the dynamic-pressure fluid bearing unit 1060 of this type, the gap between the radial projection 1069 of the shaft 1061 and the radial bearing 1062 and that between the radial projection 1069 and thrust bearing 1063 have to be extremely uniform with an accuracy as high as several micrometers for example in order to surely produce a dynamic pressure when the shaft 1061 is being rotated. If these gaps are too large, the dynamic pressure of the viscous fluid, produced in the first and second dynamic pressure producing recesses 1062a and 1062b when the shaft 1061 is rotated, will not be sufficiently effective. In addition, if the gaps are not uniform, the shaft 1061 will run out very variably.
The large gap 1070 in the bearing unit 1060 shown in FIG. 1 may cause the dynamic pressure developed due to the rotation of the shaft 1061 to be insufficient, and causes the shaft 1061 to run out very badly. To keep the viscous fluid within the housing 1064 without any leakage, the joints 1071 and 1072 between the housing and the bottom closing member 1065 and top closing member 1066 provided at the open ends of the housing 1064 are sealed with the adhesive and the top closing member 1066 is applied at the inner surface thereof with the surfactant. Because of such a construction, however, the number of parts is increased and the assembling process is complicated. Also, the sealing with the adhesive is difficult to manage and not so reliable.